SMD code 4Bs
Marking codes are not standardised, and the same code is reused by unrelated makers for unrelated parts. Below is every part in our tables printed with it, and any printed with a code that is easy to misread as it, from the manufacturers' own marking tables and published code lists.
The last letter, s, is lower case, which on NXP and Philips parts is a date or factory code, so it was set aside and 4B was searched.
80 parts are printed 4Bs
Not sure which one you have?
Answer up to 4 quick questions and these 50 parts are ranked, with a meter test that settles it. It works on a dead part too.
BC846BDWSOT-363Dual NPN transistor, 6 pins, Formosa MicrosemiDual NPN transistorSOT-3636 pinsFormosa Microsemi
- What it is
- Dual NPN transistor
- Maker
- Formosa Microsemi
- Package
- SOT-363
- Pins
- 6
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: NPN transistor pair.
BC846BDW-Q1SOT-363Dual NPN transistor, 6 pins, Formosa MicrosemiDual NPN transistorSOT-3636 pinsFormosa Microsemi
- What it is
- Dual NPN transistor
- Maker
- Formosa Microsemi
- Package
- SOT-363
- Pins
- 6
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: NPN transistor pair.
BC846BFSOT-23-6Transistor, 6 pins, YFWTransistorSOT-23-66 pinsYFW
- What it is
- Transistor
- Maker
- YFW
- Package
- SOT-23-6
- Pins
- 6
- Details
- Bipolar transistor
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: Bipolar transistor.
BC859BSOT-23Transistor, 3 pins, InfineonTransistorSOT-233 pinsInfineon
- What it is
- Transistor
- Maker
- Infineon
- Package
- SOT-23
- Pins
- 3
- Pinout
- 1 base
- 2 emitter
- 3 collector
- Details
- SMD General Purpose PNP Transistors
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: Bipolar transistor.
BC859BLSOT-23PNP transistor, 3 pins, onsemiPNP transistorSOT-233 pinsonsemi
- What it is
- PNP transistor
- Maker
- onsemi
- Package
- SOT-23
- Pins
- 3
- Details
- General Purpose Transistors Series
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: PNP transistor.
BC859BWSOT-323Transistor, 3 pins, YFWTransistorSOT-3233 pinsYFW
- What it is
- Transistor
- Maker
- YFW
- Package
- SOT-323
- Pins
- 3
- Details
- SMD General Purpose PNP Transistors
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: Bipolar transistor.
BZX384B43SOD-323Zener diode, 2 pins, VishayZener diodeSOD-3232 pinsVishay
- What it is
- Zener diode
- Maker
- Vishay
- Package
- SOD-323
- Pins
- 2
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: Zener diode.
GSRB751S-40SOD-523Schottky diode, 2 pins, Good-ArkSchottky diodeSOD-5232 pinsGood-Ark
- What it is
- Schottky diode
- Maker
- Good-Ark
- Package
- SOD-523
- Pins
- 2
- Details
- Schottky diode, 30 V, 30 mA
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: Schottky diode.
MM1Z 2V2SOD-123Zener diode, 2 pins, HottechZener diodeSOD-1232 pinsHottech
- What it is
- Zener diode
- Maker
- Hottech
- Package
- SOD-123
- Pins
- 2
- Details
- Zener diode, VZ 2.2 V
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: Zener diode.
MM1Z 2V2LSOD-123FZener diode, 2 pins, HottechZener diodeSOD-123F2 pinsHottech
- What it is
- Zener diode
- Maker
- Hottech
- Package
- SOD-123F
- Pins
- 2
- Details
- Zener diode, VZ 2.2 V
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: Zener diode.
MM1Z2V2SOD-123Zener diode, 2 pins, HXYZener diodeSOD-1232 pinsHXY
- What it is
- Zener diode
- Maker
- HXY
- Package
- SOD-123
- Pins
- 2
- Details
- Zener diode, 27 V, 0.005 A
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: Zener diode.
MM1Z2V2WSOD-123Zener diode, 2 pins, HXYZener diodeSOD-1232 pinsHXY
- What it is
- Zener diode
- Maker
- HXY
- Package
- SOD-123
- Pins
- 2
- Details
- Zener diode, 22 V, 0.005 A
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: Zener diode.
PBSS8110XSOT-89NPN transistor, 3 pins, NexperiaNPN transistorSOT-893 pinsNexperia
- What it is
- NPN transistor
- Maker
- Nexperia
- Package
- SOT-89
- Pins
- 3
- Details
- 100 V, 1 A NPN low VCEsat transistor
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: NPN transistor.
PESDNC2FD4V5BSOD-882ESD protection diode, 2 pins, PrisemiESD protection diodeSOD-8822 pinsPrisemi
- What it is
- ESD protection diode
- Maker
- Prisemi
- Package
- SOD-882
- Pins
- 2
- Details
- ESD protection diode, 4.5 V working
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: TVS or ESD protection diode.
1 more part has no package on record
NX5P2924BUKLoad switch, NXPLoad switchNot recordedNot recordedNXP
- What it is
- Load switch
- Maker
- NXP
- Package
- Not recorded
- Pins
- Not recorded
- Details
- Logic controlled high-side power switch
- Source
- Manufacturer datasheet
Is it dead? The meter test is below: Load switch.
Is it dead? One meter test per kind
Parts of the same kind are tested the same way, so each test is here once. Each part above points to its own.
NPN transistor pair
Diode range, part lifted. Test each transistor on its own pins, as the datasheet's pinout gives them.
Working, it reads
Red probe on the base reads about 0.6 to 0.75 V to the emitter and to the collector, and open the other way round. Collector to emitter reads open both ways.
Dead, it reads
- Collector to emitter the same both ways, near 0 V with a continuous beep: shorted. The commonest failure.
- The base the same both ways to another pin, near 0 V or a middling value: a shorted junction.
- Only one junction reads, or none: a junction has failed open. It then looks like a diode.
- A reading the wrong way round, where it should be open: leaky.
- On the board
- this is a first look only: the meter reads every path between those pins, and a short can be a neighbour. Lift one leg before you condemn it.
- Compare:
- If an identical part sits elsewhere on the board, measure it the same way: that is what this one should read.
- Watch for:
- A pair of diodes with a common pin reads just like a transistor, and some transistors carry a built-in diode or resistor. The datasheet says which.
A dead part still carries its marking. A short or an open says it has failed, not that it is a different part.
Bipolar transistor
Diode range, part lifted or its base leg off the pad.
Working, it reads
From the base, one probe colour reads about 0.6 to 0.75 V to the emitter and to the collector, and open the other way round. Collector to emitter reads open both ways.
Dead, it reads
- Collector to emitter the same both ways, near 0 V with a continuous beep: shorted. The commonest failure.
- The base the same both ways to another pin, near 0 V or a middling value: a shorted junction.
- Only one junction reads, or none: a junction has failed open. It then looks like a diode.
- A reading the wrong way round, where it should be open: leaky.
- On the board
- this is a first look only: the meter reads every path between those pins, and a short can be a neighbour. Lift one leg before you condemn it.
- Compare:
- If an identical part sits elsewhere on the board, measure it the same way: that is what this one should read.
- Watch for:
- A pair of diodes with a common pin reads just like a transistor, and some transistors carry a built-in diode or resistor. The datasheet says which.
A dead part still carries its marking. A short or an open says it has failed, not that it is a different part.
PNP transistor
Diode range, part lifted or its base leg off the pad.
Working, it reads
Black probe on the base reads about 0.6 to 0.75 V to the emitter and to the collector, and open the other way round. Collector to emitter reads open both ways.
Dead, it reads
- Collector to emitter the same both ways, near 0 V with a continuous beep: shorted. The commonest failure.
- The base the same both ways to another pin, near 0 V or a middling value: a shorted junction.
- Only one junction reads, or none: a junction has failed open. It then looks like a diode.
- A reading the wrong way round, where it should be open: leaky.
- On the board
- this is a first look only: the meter reads every path between those pins, and a short can be a neighbour. Lift one leg before you condemn it.
- Compare:
- If an identical part sits elsewhere on the board, measure it the same way: that is what this one should read.
- Watch for:
- A pair of diodes with a common pin reads just like a transistor, and some transistors carry a built-in diode or resistor. The datasheet says which.
A dead part still carries its marking. A short or an open says it has failed, not that it is a different part.
Zener diode
Diode range for the forward check, part lifted, red probe on the anode. A bench supply for the Zener voltage.
Working, it reads
About 0.6 to 0.8 V forward and open in reverse on the diode range. Its Zener voltage shows only on a supply: feed it through a resistor that sets about 5 mA, cathode to positive, read quickly, and it should hold near its rated voltage.
Dead, it reads
- The same reading both ways round, near 0 V with a continuous beep or the same middling value: shorted.
- Open both ways, forward too: failed open.
- Holds well off its rated voltage on the supply test: drifted.
- A soft knee, or a voltage that creeps on the supply test: leaky.
- On the board
- this is a first look only: the meter reads every path between those pins, and a short can be a neighbour. Lift one leg before you condemn it.
- Compare:
- If an identical part sits elsewhere on the board, measure it the same way: that is what this one should read.
- Watch for:
- A meter's diode range stops at about 2 to 3 V, so almost every Zener reads open in reverse on it, good or bad; a 3 V meter may just show a 2.4 or 2.7 V part. Above about 3 V the meter cannot tell a Zener from a plain diode.
A dead part still carries its marking. A short or an open says it has failed, not that it is a different part.
Schottky diode
Diode range, part lifted or one leg off the pad. Red probe on the anode.
Working, it reads
About 0.15 to 0.45 V anode to cathode, roughly half a silicon diode, and open the other way.
Dead, it reads
- The same reading both ways round, near 0 V with a continuous beep or the same middling value: shorted.
- A reading the wrong way round as well: leaky.
- Open both ways: failed open.
- On the board
- this is a first look only: the meter reads every path between those pins, and a short can be a neighbour. Lift one leg before you condemn it.
- Compare:
- If an identical part sits elsewhere on the board, measure it the same way: that is what this one should read.
- Watch for:
- A large Schottky can read about 0.1 V forward and beep like a short, and leaks a little the wrong way when good, more when warm. It is shorted only if it reads the same both ways. Measure it cold, beside an identical cold one.
A dead part still carries its marking. A short or an open says it has failed, not that it is a different part.
Load switch
Voltage, board powered, black probe on ground.
Working, it reads
Switched on, the output pin sits at the input voltage. Switched off, it sits near 0 V.
Dead, it reads
- Output at the input voltage while switched off: the pass element has shorted.
- Input present and switched on, no output: failed open, or shut down into a shorted load. Power off and measure output to ground.
- On the board:
- An output near 0 Ω to ground is usually the load. Lift the output pin to see which.
- Compare:
- If an identical part sits elsewhere on the board, measure it the same way: that is what this one should read.
- Watch for:
- The pinout and whether the enable is active high or low differ between parts. The datasheet gives both.
A dead part still carries its marking. A short or an open says it has failed, not that it is a different part.
NPN transistor
Diode range, part lifted or its base leg off the pad.
Working, it reads
Red probe on the base reads about 0.6 to 0.75 V to the emitter and to the collector, and open the other way round. Collector to emitter reads open both ways.
Dead, it reads
- Collector to emitter the same both ways, near 0 V with a continuous beep: shorted. The commonest failure.
- The base the same both ways to another pin, near 0 V or a middling value: a shorted junction.
- Only one junction reads, or none: a junction has failed open. It then looks like a diode.
- A reading the wrong way round, where it should be open: leaky.
- On the board
- this is a first look only: the meter reads every path between those pins, and a short can be a neighbour. Lift one leg before you condemn it.
- Compare:
- If an identical part sits elsewhere on the board, measure it the same way: that is what this one should read.
- Watch for:
- A pair of diodes with a common pin reads just like a transistor, and some transistors carry a built-in diode or resistor. The datasheet says which.
A dead part still carries its marking. A short or an open says it has failed, not that it is a different part.
TVS or ESD protection diode
Diode range, from the protected line to ground, part lifted if you can.
Working, it reads
A one-way part reads about 0.6 to 0.8 V forward and open in reverse. A two-way part reads open both ways. Arrays with several lines read as the datasheet's diagram draws them.
Dead, it reads
- From the line to ground, the same reading both ways, near 0 V with a continuous beep: shorted.
- A reading both ways on a one-way part: leaky.
- A one-way part open both ways: failed open.
- On the board
- , a line reading shorted to ground can be this part or anything else on that line. Lift it: if the short goes with it, it has failed.
- Compare:
- The same part on the next line or connector pin is the healthy reading to compare with.
- Watch for:
- A two-way part reads open both ways when it is good, exactly like one that has failed open. The meter cannot tell them apart; an identical part on the next line can.
A dead part still carries its marking. A short or an open says it has failed, not that it is a different part.
Printed with a code easy to misread as 4Bs
One character differs, and it is one that is easy to confuse under a lamp. Each code has a page of its own.
Codes not listed here are printed on 2 more parts.
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